PNEUMATICS
AIR CONDITIONING
AND PRESSURIZATION
AIRPLANE
OPERATIONS
MANUAL
2-14-10
Page
2
Code
01
REVISION 38
AOM-145/1114
ECU OPERATION
Each ECU consists of a dual heat exchanger, an air cycle machine
(compressor, turbine, and fan), a condenser, a water separator and
related control and protective devices, installed forward of the airplane
wing root, inside the wing-to-fuselage fairing.
The automatically-controlled bleed air from the pneumatic system
supplies the ECU. Downstream pressure is regulated by the Pack
Valve (Pressure Regulating and Shutoff Valve).
After the Pack Valve, the airflow is divided into two lines:
- One cold line that passes through to the Air Cycle Machine.
- One hot line that bypasses the Air Cycle Machine.
Both airflow lines are gathered at the expansion turbine discharge.
In the Air Cycle Machine (ACM), air is cooled in the primary heat
exchanger and passes through the compressor, thus causing a
pressure increase. The air then goes to the secondary heat exchanger
where it is cooled again.
After leaving the secondary heat exchanger, the high-pressure cooled
air passes through a condenser and a water separator for condensed
water removal. Spray nozzles uses the separated water to improve the
heat exchanger efficiency.
The main airstream is ducted to the turbine and expanded to provide
power for the compressor and cooling fan. This energy removal
produces very low turbine discharge temperatures, achieving
adequate low temperatures in the process.
The cold exit air is mixed with warm air supplied by the recirculation
fan and/or with the hot bypass air immediately upon leaving the
turbine. A check valve is provided in the recirculation duct to prevent
reverse flow if the recirculation fan is inoperative.
The ECU outlet air temperature is controlled through the dual
temperature control valve. One valve adds hot bleed air to the turbine
discharge while the other valve restricts the compressor inlet flow.
The ECUs are cooled in flight by external ACM fans, using the external
ram air. On the ground, the ECUs are cooled by the ACM fans only.
The system has emergency ventilation, as an alternate means to allow
the outside air into the cabin. The impact air passes through the same
ram air inlets that are used to cool the dual heat exchangers.
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